This invention is a pre-formed intrastromal corneal insert. It is made of a physiologically compatible polymer and may be used to adjust corneal curvature and thereby correct vision abnormalities. The insert or segment may also be used to deliver therapeutic or diagnostic agents to the interior of the cornea or of the eye. The insert subtends only a portion of a ring, or xe2x80x9carcxe2x80x9d, encircling the anterior cornea outside of the cornea""s field of view but within the frontal circumference of the cornea, but may be used in multiples to form complete arcs or to form constructs of varying thickensses. The invention also includes both a minimally invasive procedure for inserting one or more of the devices into the cornea as well as the thus-corrected eye.
Anomalies in the overall shape of the eye can cause visual disorders. Hyperopia (xe2x80x9cfarsightednessxe2x80x9d) occurs when the front-to-back distance in the eyeball is too short. In such a case, parallel rays originating greater than 20 feet from the eye focus behind the retina. In contrast, when the front-to-back distance of eyeball is too long, myopia (xe2x80x9cnearsightednessxe2x80x9d) occurs and the focus of parallel rays entering the eye occurs in front of the retina. Astigmatism is a condition which occurs when the parallel rays of light do not focus to a single point within the eye, but rather have a variable focus due to the fact that the cornea refracts light in a different meridian at different distances. Some degree of astigmatism is normal, but where it is pronounced, the astigmatism must be corrected.
Hyperopia, myopia., and astigmatism are usually corrected by glasses or contact lenses. Surgical methods for the correction of such disorders are known. Such methods include radial keratotomy (see, e.g., U.S. Pat. Nos. 4,815,463 and 4,688,570) and laser corneal ablation (see, e.g., U.S. Pat. No. 4,941,093).
Another method for correcting those disorders is through the implantation of polymeric rings (intrastromal corneal rings or) in the eye""s corneal stroma to change the curvature of the cornea. Previous work involving the implantation of polymethylmethacrylate (PMMA) rings, allograft corneal tissue, and hydrogels is well documented. One of the ring devices involves a split ring design which is inserted into a channel previously dissected in the stromal layer of the cornea. A minimally invasive incision is used both for producing the channel and for inserting the implant. See, for instance, the use of PMMA intrastromal rings in U.S. Pat. No. 4,452,235 to Reynolds; U.S. Pat. No. 4,671,276 to Reynolds; U.S. Pat. No. 4,766,895 to Reynolds; and U.S. Pat. No. 4,961,744 to Kilmer et al. These documents suggest only the use of intrastromal corneal rings which completely encircle the cornea.
The use of soft polymers as intrastromal inserts is not widely known. For instance, U.S. Pat. No. 5,090,955 to Simon, suggests an, which is made by introducing a settable polymer or gel into a previously made intrastromal channel. This procedure does not allow the surgeon to specify the precise size of the resulting ring nor is it a process which allows precise control of the pathway of the flowing polymer within the eye since the gel must simply conform to the shape of the intrastromal channel. However, it does show the concept of using arcuate channels containing a gel-based insert centered about the corneal to correct.
Temirov et al, xe2x80x9cRefractive circular tunnel keroplasty in the correction of high myopiaxe2x80x9d, Vestnik Oftalmologii. 1991: 3-21-31, suggests the use of collagen thread as intrastromal corneal ring material.
These publications do not suggest the introduction of pre-formed polymeric arcuate inserts into the cornea for the correction of various visual aberrations. Certainly the publications do not imply that the devices may be used to introduce therapeutic or diagnostic materials into the corneal intrastromal space.
This invention is a pre-formed polymeric insert suitable for insertion between the lamella of the corneal stroma. The insert is an arc-shaped segment of a ring and may be used in isolation, in isolated multiples, in cooperative multiples, as segments in a larger assemblage encircling at least a portion of the cornea, or as assemblages to form constructs of varying thickness. The insert may be of one or more synthetic or natural polymers, hydrophilic or hydrophobic, or may be a hybrid device comprising layered materials or it may be hollow.
The insert may be adapted to be fillable with a biologic agent, drug or other liquid, emulsified, or time-release eye treatment or diagnostic material.
When the insert is a hybrid, both the inner and outer portions may comprise variously one or more high or low modulus, physiologically compatible polymers or a composite of a low modulus polymer and a high modulus polymer. The inner portion may comprise a gel or a polymeric material which is polymerized in situ after introduction into a hollow center layer.
These inventive segmented inserts may be introduced into the corneal stroma using techniques involving the steps of providing an intrastromal channel which traverses at least a portion of the circumcorneal rotation. Specific indications, such as astigmatism, may be rectified by insertion of one or more of the inserts into a partial intrastromal channel to flatten the steeper portions of the anterior corneal surface without insertion of a complete intrastromal corneal ring (or intracorneal ring).
If hydratable polymers are used, they may be hydrated before or after introduction into the intrastromal passageway created by the surgical device used to introduce these devices into the eye. If the outer layer is hydrated before insertion into the eye, the final size of the insert is set before that insertion. If the hydratable polymers are allowed to hydrate within the corneal space, the device (if appropriate polymers are chosen) will swell within the eye to its final size. If prehydrated, the outer layer often provides a measure of lubricity to the device, allowing it to be inserted with greater ease. Other of the noted low modulus polymers may also provide such lubricity.